Photoreflectance spectroscopy of BiOCl epitaxial thin films

TL;DR

This study reports the discovery of a new optical transition in BiOCl thin films, revealing excitonic effects and temperature dependence, and compares its phononic properties with other semiconductors.

Contribution

It presents the first observation of a new optical transition in BiOCl epitaxial thin films and analyzes its excitonic nature and temperature dependence.

Findings

Identification of a new optical transition close to the bulk critical point

Evidence of excitonic effects in BiOCl thin films

Temperature dependence of the optical anomaly analyzed with Varshni model

Abstract

We have observed a new optical transition in the photoreflectance spectra of indirect-gap BiOCl thin films, which were grown on SrTiO$_3$ substrates. The position of this transition is close in energy to its bulk critical point energy. Moreover, these are significantly lower than a higher-lying direct-type critical point from an energetic point of view. The spectral line shape analysis for our observed signal suggests the presence of an excitonic effect of this compound. We determined its dependence of the optical anomaly on temperature ranging from 80 K to room temperature. We adopted the Varshni model for this analysis. At last, we compared phononic properties of BiOCl with those of an element and binary semiconductors.